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Documentation: point to key_custom instead of key_ext

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Replace references to the deprecated functions `psa_generate_key_ext()` and
`psa_key_derivation_output_key_ext()` by their replacements
Implement `psa_generate_key_custom()` and
`psa_key_derivation_output_key_custom()`.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
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Gilles Peskine
2024-06-06 21:23:00 +02:00
parent a8e39f2156
commit 603b5b842b
2 changed files with 16 additions and 16 deletions
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docs/psa-transition.md
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@@ -779,7 +779,7 @@ A finite-field Diffie-Hellman key can be used for key agreement with the algorit
The easiest way to create a key pair object is by randomly generating it with [`psa_generate_key`](https://mbed-tls.readthedocs.io/projects/api/en/development/api/group/group__random/#group__random_1ga1985eae417dfbccedf50d5fff54ea8c5). Compared with the low-level functions from the legacy API (`mbedtls_rsa_gen_key`, `mbedtls_ecp_gen_privkey`, `mbedtls_ecp_gen_keypair`, `mbedtls_ecp_gen_keypair_base`, `mbedtls_ecdsa_genkey`), this directly creates an object that can be used with high-level APIs, but removes some of the flexibility. Note that if you want to export the generated private key, you must pass the flag [`PSA_KEY_USAGE_EXPORT`](https://mbed-tls.readthedocs.io/projects/api/en/development/api/group/group__policy/#group__policy_1ga7dddccdd1303176e87a4d20c87b589ed) to [`psa_set_key_usage_flags`](https://mbed-tls.readthedocs.io/projects/api/en/development/api/group/group__attributes/#group__attributes_1ga42a65b3c4522ce9b67ea5ea7720e17de); exporting the public key with [`psa_export_public_key`](https://mbed-tls.readthedocs.io/projects/api/en/development/api/group/group__import__export/#group__import__export_1gaf22ae73312217aaede2ea02cdebb6062) is always permitted.
For RSA keys, `psa_generate_key` uses 65537 as the public exponent. You can use [`psa_generate_key_ext`](https://mbed-tls.readthedocs.io/projects/api/en/development/api/group/group__random/#group__random_1ga6776360ae8046a4456a5f990f997da58) to select a different public exponent. As of Mbed TLS 3.6.0, selecting a different public exponent is only supported with the built-in RSA implementation, not with PSA drivers.
For RSA keys, `psa_generate_key` uses 65537 as the public exponent. You can use [`psa_generate_key_custom`](https://mbed-tls.readthedocs.io/projects/api/en/development/api/group/group__random/#ga0415617443afe42a712027bbb8ad89f0) to select a different public exponent. As of Mbed TLS 3.6.1, selecting a different public exponent is only supported with the built-in RSA implementation, not with PSA drivers.
To create a key object from existing material, use [`psa_import_key`](https://mbed-tls.readthedocs.io/projects/api/en/development/api/group/group__import__export/#group__import__export_1ga0336ea76bf30587ab204a8296462327b). This function has the same basic goal as the PK parse functions (`mbedtls_pk_parse_key`, `mbedtls_pk_parse_public_key`, `mbedtls_pk_parse_subpubkey`), but only supports a single format that just contains the number(s) that make up the key, with very little metadata. The table below summarizes the PSA import/export format for key pairs and public keys; see the documentation of [`psa_export_key`](https://mbed-tls.readthedocs.io/projects/api/en/development/api/group/group__import__export/#group__import__export_1ga668e35be8d2852ad3feeef74ac6f75bf) and [`psa_export_public_key`](https://mbed-tls.readthedocs.io/projects/api/en/development/api/group/group__import__export/#group__import__export_1gaf22ae73312217aaede2ea02cdebb6062) for more details.